Abstract

Background

Chemotherapeutic treatment results in chronic pain in an estimated 30-40 percent of
patients. Limited and often ineffective treatments make the need for new therapeutics
an urgent one. We compared the effects of prophylactic cannabinoids as a preventative
strategy for suppressing development of paclitaxel-induced nociception. The mixed
CB1/CB2 agonist WIN55,212-2 was compared with the cannabilactone CB2-selective agonist AM1710, administered subcutaneously (s.c.), via osmotic mini pumps
before, during, and after paclitaxel treatment. Pharmacological specificity was assessed
using CB1 (AM251) and CB2 (AM630) antagonists. The impact of chronic drug infusion on transcriptional regulation
of mRNA markers of astrocytes (GFAP), microglia (CD11b) and cannabinoid receptors
(CB1, CB2) was assessed in lumbar spinal cords of paclitaxel and vehicle-treated rats.

Results

Both WIN55,212-2 and AM1710 blocked the development of paclitaxel-induced mechanical
and cold allodynia; anti-allodynic efficacy persisted for approximately two to three
weeks following cessation of drug delivery. WIN55,212-2 (0.1 and 0.5 mg/kg/day s.c.)
suppressed the development of both paclitaxel-induced mechanical and cold allodynia.
WIN55,212-2-mediated suppression of mechanical hypersensitivity was dominated by CB1 activation whereas suppression of cold allodynia was relatively insensitive to blockade
by either CB1 (AM251; 3 mg/kg/day s.c.) or CB2 (AM630; 3 mg/kg/day s.c.) antagonists. AM1710 (0.032 and 3.2 mg/kg /day) suppressed
development of mechanical allodynia whereas only the highest dose (3.2 mg/kg/day s.c.)
suppressed cold allodynia. Anti-allodynic effects of AM1710 (3.2 mg/kg/day s.c.) were
mediated by CB2. Anti-allodynic efficacy of AM1710 outlasted that produced by chronic WIN55,212-2
infusion. mRNA expression levels of the astrocytic marker GFAP was marginally increased
by paclitaxel treatment whereas expression of the microglial marker CD11b was unchanged.
Both WIN55,212-2 (0.5 mg/kg/day s.c.) and AM1710 (3.2 mg/kg/day s.c.) increased CB1 and CB2 mRNA expression in lumbar spinal cord of paclitaxel-treated rats in a manner blocked
by AM630.

Conclusions and implications

Cannabinoids block development of paclitaxel-induced neuropathy and protect against
neuropathic allodynia following cessation of drug delivery. Chronic treatment with
both mixed CB1/CB2 and CB2 selective cannabinoids increased mRNA expression of cannabinoid receptors (CB1, CB2) in a CB2-dependent fashion. Our results support the therapeutic potential of cannabinoids
for suppressing chemotherapy-induced neuropathy in humans.